Whistleblower Maurice McCabe warned then justice minister Dermot Ahern five years ago that the scale of corruption within the Garda was like "Donegal all over again".

Referring to the shocking revelations that came out of the epic Morris Tribunal, the sergeant appealed for an independent inquiry after a senior officer publicly dismissed any suggestion of wrongdoing within his ranks.

The Government-ordered report into his dossier of allegations has found Alan Shatter, who resigned on Wednesday over the scandal, accepted without question Garda Commissioner Martin Callinan's insistence there was no case against him.

Furthermore, there was no evidence of any serious examination of Sgt McCabe's disturbing allegations by Department of Justice officials, and virtually no records could be found of any decisions or advice taken on the case.

Barrister Sean Guerin, who investigated the handling of the case, said it was unclear what - if any - action was taken by Mr Shatter and his department over the Garda corruption claims other than to ask the force chief for his view.

"In effect, the process of determining Sergeant McCabe's complaint went no further than the Minister receiving and acting upon the advice of the person who was the subject of the complaint," he found.

While it is reasonable to ask the subject of a complaint for their response "it is a different matter altogether to be entirely satisfied by that response", he concluded in a 300-page report on the affair.

Evidence from the Department of Justice also reveals Sgt McCabe's wife Lorraine pleaded with Mr Shatter three years ago to help them, describing the "hurt, stress, annoyance, severe damage and sheer hell on our family and our family life".

Despite her emotional detailing of a death threat against her husband from a member of the force - about which Sgt McCabe's father also made an official complaint - and insistence on a cover-up, she was directed to the Garda Ombudsman.

The watchdog does not deal with internal Garda complaints between colleagues.

When she wrote back saying she asked for help but got none and asked for an acknowledgement that the allegations were extremely serious, Mr Shatter's secretary replied that it would be brought to his attention.

In his report, Mr Guerin says he could not make sense of another letter in 2011 from Mr Shatter to Sgt McCabe's solicitor about a Garda Ombudsman probe - which never took place - into his allegations of wrongdoing.

The whistleblower first wrote to Mr Ahern in March 2009 urging an independent inquiry after his Superintendent Colm Rooney was reported in the local newspaper dismissing as "absolute rubbish" claims of serious malpractice within his ranks.

In his letter, he said it was like "Donegal all over again".

But Mr Ahern's private secretary replied two months later that it was best to leave the Garda Commissioner to complete his work, referring to an internal probe.

The meeting at the Hillgrove Hotel in Monaghan ended up in a "physical confrontation" as the whistleblower tried to leave with his box of records, which Asst Comm Byrne demanded he hand over.

The report says he handed over the evidence for fear of being assaulted, but the public prosecutor directed no prosecution after a formal complaint alleging assault and false imprisonment.

The investigation details letters between Sgt McCabe, his solicitors and the Department of Justice spanning five years and two justice ministers.

In one letter, the whistleblower makes an official complaint about the Garda Commissioner Martin Callinan putting a superintendent at the centre of some allegations on a promotion list.

"It has sent out a message to the force that if you ignore your duty, are grossly negligent, hide and cover up, you will deemed suitable for promotions," he wrote.

The only action of Mr Shatter was to seek a response from Mr Callinan which was "accepted without question", it was found.

Furthermore, the report accuses the Garda chief of dismissing most of the detailed allegations or corruption and malpractice in a single paragraph.

Sgt McCabe repeatedly called for an independent investigation, either under the Garda Siochana Act or the Commission of Investigations Act - both of which give the minister the power to establish a special inquiry in the public interest, the records show.

He provided evidence and offered to make a sworn statement, adding that he had lost all confidence in the force to investigate itself.

But Mr Guerin says the contact ended in an impasse after February last year.

"There appears to be no question of the allegations having been investigated at the instigation of the minister," he said, adding it was not clear if any action was taken.

In a swipe at the Department of Justice, he said there was no evidence it understood the minister's "significant role" in such cases.

Official simply referred complaints to the Garda itself.

"I can find no evidence of any detailed assessment within the Department of any allegations made by Sgt McCabe or of the response received by the Commissioner," Mr Guerin found.

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